The present invention relates to a system for controlling the clutch torque of an electromagnetic clutch disposed between the crankshaft of an engine and the transmission of a motor vehicle.
A clutch torque control system for starting and deceleration of a vehicle is, for example, disclosed in Japanese Patent Laid Open No. 57-15024. In this system, the clutch current flowing in a coil of the clutch exponentially increases with respect to the increase of the engine speed for starting the vehicle. When vehicle speed exceeds a predetermined speed (for example 20 km/h), lock-up current flows through the coil, so that the clutch is completely engaged. Upon the deceleration of the vehicle, when the vehicle speed decreases below the predetermined speed, the clutch current is cut off to disengage the clutch.
In such a control system, if the accelerator pedal of the vehicle is depressed for acceleration of the vehicle in the disengage condition of the clutch at a low vehicle speed, the clutch current is passed through the coil in dependency on the engine speed in a similar way as when starting the vehicle. In such an acceleration condition, the driven shaft of the clutch is rotated, by rotating wheels of the vehicle, through the transmission. The rotation speed of the driven shaft is determined by the vehicle speed and transmission ratio at that time. When the speed of the drive member of the clutch is much lower than the speed of the driven member when engaging the clutch, the vehicle is braked by the engine operation, resulting in a decrease in the vehicle speed.